a very fair skin of it. Before noon I climbed to the rim rock on N.E. side collecting specimens of the tufa all the way. I can see no differentiation in composition or structure, but the upper part is much harder and darker colored, with a tendency towards pink and red everywhere. However, between the cap of the cliff and the next ledge above there is a white zone perhaps 20 or 30 ft thick showing on both sides of the canyon. One or two big pieces of tufa had a metallic ring when struck, but were quite soft except a thin outer coat. Angular fragments of older rocks are included in the tufa all the way up. I collected some of these. The harder weathered coating on the tufa, both upper and lower, is very thin, perhaps from 1/8 to 1/2 inch, not usually well enough defined for measurement. From the rim of the canyon there is a fine view of the mesa S.W. of the canyon, with the mountains in
